The field of the invention is numerical control systems for machine tools, and particularly, control systems such as that described in U.S. Pat. No. 4,038,533 entitled "Industrial Control Processor System."
Numerical control systems connect to machine tools to control the motion of a cutting tool in response to a stored part program which directs the machine through a series of steps. In a milling machine, for example, the cutting tool may be moved along three separate axes to make straight line or circular cuts in a work piece, and the part program is a series of directions stored as digital numbers and codes which indicate where the cuts are to be made and in what sequence they are to be made. Although the part programs have traditionally been stored on magnetic or punched tape and have been read into the numerical control system in blocks of data as they are being executed, more recent numerical control systems store entire part programs in their random access memories.
In addition to controlling the motions of a cutting tool, numerical control systems also control auxiliary functions on the machine such as tool selection and changing, spindle speed, coolant flow, pallet selection and changing. These auxiliary functions vary considerably from machine to machine and they have typically been performed by separate hardwired logic circuits which respond both to sensed conditions on the machine tool and to directions indicated by selected codes within the part program. As exemplified by the above cited U.S. Pat. No. 4,038,533 and U.S. Pat. No. 3,810,104 entitled "Programmable Magnetics for a Numerical Control System," in recent years programmable controllers have been interfaced with the numerical control system processor to control the auxiliary functions. Such programmable controllers may be a separate programmed processor or an integral part of the numerical control system processor.
The addition of a programmable controller to a numerical control system provides a number of very practical advantages. First, the programmable controller hardward need not be changed when integrating the numerical control system to various types of machine tools. Instead, the programmable controller is programmed to enable it to interface with a particular machine. Second, although programmable interfaces have been available for many years in minicomputer-based numerical control systems, a programmable controller is much easier for the user to program because of the instruction set which is employed and the editing features which are available on programmable controllers.
Despite the many advantages of interfacing a programmable controller to a numerical control system, it does add cost to the system, and in some cases this added cost cannot be justified. For example, in some applications the machine tool to which the control is interfaced is very simple and the job of developing and building a separate logic circuit or relay circuit to operate the discrete I/O devices is trivial. It is desirable, therefore, that a numerical control system provide the programmable controller interface as an optional feature rather than an inseparable part of the basic numerical control system.
The vast majority of numerical control systems in service are constructed of discrete digital electronic components such as logic gates, latches, flip-flops and reigsters. In recent years, however, minicomputers or industrial computers, such as that disclosed in the above cited U.S. Pat. No. 4,038,533 have been programmed to carry out the numerical control functions. With the advent of relatively fast and inexpensive microprocessors, microprocessor-based numerical control systems are now economically and technically feasible.
Numerical control systems include a processor which converts blocks of part program data into motion command signals which are output to servomechanisms on a machine. In addition, codes in the part program are converted to logic signals which control the discrete I/O devices on the machine to perform auxiliary functions. The operation of the numerical control system is controlled through numerous switches and display devices which are mounted on a front panel where they are accessible to the machine operator. Keyboards and CRT displays are also commonly associated with the front panel to enable entry of manual data and editing of part program data. Numerous connections are required between these front panel devices and the numerical control processor. Such connections are expensive to make and as a practical matter this requires that the front panel and the numerical control processor be located as close as possible to each other. As a result, most numerical control systems are housed in a large cabinet with the front panel controls disposed on its front. The cabinet is positioned for the convenience of the operator and considerable wiring is required between the free-standing numerical control cabinet and the machine which it controls.